1. Field of the Invention
The present invention relates to an image forming device such as a copying machine, a printer, and a facsimile machine.
2. Description of the Related Art
A known electrophotographic image forming device uses, for example, a photoconductive drum as an image carrier. In such an image forming device, a surface of a charged photoconductive drum is exposed by a laser light, and an electrostatic latent image is formed. Toner adheres to the electrostatic latent image, and the electrostatic latent image is visualized. The visualized image is transferred onto paper, and an image is formed. There exists a demand for an improvement of an image quality in such an image forming device. Accompanying this demand, an improvement in the accuracy of an exposed position of the laser light with respect to the photoconductive drum has been important. However, if errors accumulate in component accuracy or in assembly of the photoconductive drum or an exposing device, which outputs the laser light, accuracy of the exposed position of the laser light with respect to the photoconductive drum decreases. As a result, defects, such as an inclination of an image with respect to a recording paper, are generated. Therefore, after mounting the exposing device, a mounted position of the exposing device is adjusted to improve the accuracy of the exposed position of the laser light with respect to the photoconductive drum.
According to a conventional method for adjusting a mounted position of an exposing device, for example, a fine adjustment is carried out by adding a shim for a position adjustment to the mounted position. When adjusting the mounted position by using the shim, after adding the shim and fixing the exposing device with a screw, it is necessary to check whether or not the accuracy of the position has improved. Therefore, when the accuracy of the position has not improved as expected, it is necessary to remove the fixed screw and replace with a shim having a different thickness and fix the screw again. Each time the shim is replaced, a troublesome operation must be performed because the screw must be removed and then fixed again.
As conventional methods other than the method using the shim for adjusting the position, for example, there are the following two methods. According to a first conventional method, a printer unit includes a Laser Scanning Unit (LSU) and a photoconductive drum, in this order from an upper portion of a frame, and two bar-shaped members are arranged parallel to a driving shaft core of the photoconductive drum and are spaced away from one another by an appropriate distance in a horizontal direction in an upper portion of the printer unit within the frame. The LSU, which is positioned by the bar-shaped members in the same manner, is also positioned highly accurately with respect to the photoconductive drum.
According to a second conventional method, an optical writing unit includes a laser light source and irradiates a light from the laser light source onto a surface of a photoconductive drum via a reflecting mirror. A unit frame including the laser light source and the reflecting mirror are held inside an image forming device such that the unit frame can be pivoted within a plane parallel to an axial line direction of the photoconductive drum. In addition, the rotation of the unit frame is controlled by a cam, which rotates by being driven by a motor, and an elastic member, which urges the unit frame against a cam surface.
According to the first conventional method, the LSU is positioned highly accurately with respect to the photoconductive drum. However, there are cases where after assembling the LSU, the position of the LSU is displaced due to a lack of component accuracy or an accumulated error of the frame itself on which the LSU is mounted or other parts, or the position of the LSU is displaced as a result of a change over time of the frame or the like, or due to vibration. In these cases, since the first conventional method does not provide a mechanism for adjusting the position after the assembling, an exposing position of the LSU cannot be adjusted easily when the accuracy of the exposing position of the LSU has decreased. According to the second conventional method, since the position of the optical unit is adjusted by using the cam, the entire unit is configured to rotate. As a result, it is difficult to make a fine adjustment, and after making an adjustment, the entire unit is prone to move, making the accuracy unstable.